1. Field of the Invention
The present invention relates to a process for producing an acrylic ester, and more particularly, to a process for producing an acrylic ester from acrylic acid and an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms using a strongly acidic cation exchange resin.
2. Description of the Related Art
Acrylic esters can be produced from acrylic acid and various alcohols, for example, as disclosed in Japanese Patent Publication No. Shou 52-57116, by an esterification reaction using a homogeneous catalyst such as sulfuric acid or phosphoric acid, or alternatively, for example, as disclosed in Japanese Patent Laid-open Publications Nos. Hei 2-279655 and Hei 3-52843, by an esterification reaction using a heterogeneous catalyst such as a strongly acidic cation exchange resin.
In the continuous production of an acrylic ester, there have heretofore been carried out operations in which acrylic acid and an alcohol are esterified in a reactor using a catalyst such as an inorganic acid, e.g., sulfuric acid or phosphoric acid, or a strongly acidic cation exchange resin, the resulting reaction liquid is supplied to a low-boiling separation column to separate it into a high-boiling substance composed mainly of a generated acrylic ester and a low-boiling component composed mainly of an unreacted alcohol, acrylic acid, and generated water, and an acrylic ester is collected from the former high-boiling substance and circulated to the reaction system.
In a process using an inorganic acid such as sulfuric acid or phosphoric acid as an esterification catalyst (e.g., see Japanese Patent Laid-open Publication No. Shou 52-57116), the use of a highly corrosive inorganic acid has no other choice to select an anti-corrosive material for apparatus, which causes problems that the apparatus becomes expensive and the waste liquid treatment to make an inorganic acid contained in the waste liquid harmless becomes highly costly.
In an esterification reaction using an ion exchange resin, there is no drawback that will be involved when an inorganic acid is used as an esterification catalyst. As for acrylic acid to be used as a raw material, acrylic acid purified to remove low-boiling impurities and high-boiling impurities is used, the production cost of acrylic acid rises due to the removal of high-boiling impurities, and therefore, the use of unpurified acrylic acid would become advantageous. However, when acrylic acid containing a high-boiling acid component is used as a raw material, unfavorable polymerization reaction and side reaction occur, facilities such as piping systems are clogged by polymers, the unit consumption of acrylic acid or an alcohol increases, and the quality of a product is deteriorated. Thus, in Japanese Patent Laid-open Publication No. 2003-171347, there is proposed a countermeasure that the concentration of impurities such as maleic acid, β-acryloxypropionic acid (i.e., a dimer of acrylic acid), furfural, and benzaldehyde is restricted to a specific concentration or lower.
Of these high-boiling impurities, in particular, high-boiling acid components such as maleic acid and β-acryloxypropionic acid can easily be removed from waste oil in the production of an ester using a low-boiling alcohol having 4 or less carbon atoms as a raw material, thereby causing no particular problem. However, in the production of an ester using an aliphatic or alicyclic alcohol having from 5 to 8 carbon atoms as a raw material, it is difficult to separate high-boiling acid components, which has remarkable influences on the loss in quality of a product and the deterioration of the unit consumption of the main raw material, and which requires uneconomical operation, thereby causing serious problems. In particular, β-acryloxypropionic acid is generated during the storage after the acrylic acid production process, and therefore, the control of temperature and the like during the storage are sometimes required, which makes it difficult to maintain the stable quality and the low unit consumption of raw materials in the production of an acrylic ester.